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Author Topic:   Is Faster Than Light travel the wrong question?
kbertsche
Member (Idle past 2122 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 5 of 81 (533286)
10-29-2009 7:34 PM
Reply to: Message 1 by Michamus
10-29-2009 10:43 AM


quote:
So my question is this, is FTL or LS travel really what we are after? What prevents us from traveling at 600,000km/sec, seeing as from our FoR light is still traveling at light-speed?
What is your goal? What are you trying to achieve?
Meldinoor explained things pretty well, I think. At near the speed of light you could travel a large distance without aging very much. You would want to accelerate as fast as tolerable for as long as possible, perhaps even for half the travel time, then decelerate the same way. An acceleration of 1G for 1 year would give a relative velocity of about 0.7 c, and you would age at about 70% the normal rate. You'd need multi-G's of acceleration for multi-years to get large factors of time dilation.
The energy expenditure for this would be enormous, of course. That's why sci-fi scenarios of sending people to colonize distant planets are complete fantasy. It would require an energy source which is nearly infinite and essentially free.
Edited by kbertsche, : Bad back-of-envelope calculation.
Edited by kbertsche, : Added correct values for 1G and 1 year.

This message is a reply to:
 Message 1 by Michamus, posted 10-29-2009 10:43 AM Michamus has replied

Replies to this message:
 Message 6 by Taz, posted 10-30-2009 12:20 AM kbertsche has replied
 Message 19 by Michamus, posted 10-31-2009 8:01 AM kbertsche has replied

  
kbertsche
Member (Idle past 2122 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 9 of 81 (533365)
10-30-2009 11:45 AM
Reply to: Message 6 by Taz
10-30-2009 12:20 AM


fantasy
quote:
Rrhain and I had a similar argument about this very thing. Here is my perspective on the matter of interstellar travel. But first, I need to reiterate what you said in terms that people from the age of sails could understand.
The wind speed to carry a ship from Europe to North America in a few days would be enormous, of course. That's why sci-fi scenarios of sending people to distant lands are complete fantasy. It would require wind speed that is nearly impossible to imagine.
You lock your mindset into a particular technology (wind power). I specifically did NOT do this.
In addition, your analogy is poor. The wind speed wouldn't need to be unimaginably high, just high and steady.
quote:
If it's not obvious yet, I'm trying to point out that you are approaching this problem with a very 20th-21st century way of thinking, just like how a person from the 16th century would think about intercontinental travel. Flight never occurred to them. Bullet train never occurred to them. Underwater tunnels never occurred to them. To them, getting from Europe to the Americas or Asia in less than several months time would be nothing more than fantasy.
No. My comments are not locked into "20th-21st century way of thinking." They are locked into physical reality. But they allow for new energy sources.
quote:
In very much the same way, you're superimposing our limited understanding of physics onto all the great inventions and discoveries waiting for us in the future. Sure, it may be fantasy now, but who knows what the future holds?
No. My comments do not depend on "our limited understanding of physics." I have explicitly left room for new energy sources and new physics by saying that this "would require an energy source which is nearly infinite and essentially free."
For a society which is worried about energy costs and limited energy availability, sending large groups of people to colonize distant planets is pure fantasy. Doing so would require a new energy source, and we would no longer be a society which is worried about energy costs and limited energy availability.

This message is a reply to:
 Message 6 by Taz, posted 10-30-2009 12:20 AM Taz has replied

Replies to this message:
 Message 11 by Taz, posted 10-30-2009 12:20 PM kbertsche has replied

  
kbertsche
Member (Idle past 2122 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 14 of 81 (533385)
10-30-2009 2:03 PM
Reply to: Message 11 by Taz
10-30-2009 12:20 PM


Re: fantasy
quote:
There you go again, superimposing our limited understanding of physics to future inventions and discoveries.
No. I am superposing reality and what we know of physics.
quote:
Just like the people in the 16th century who couldn't imagine any other way to travel from continent to continent other than by sail boats, you are locked into this mindset that interstellar travel can't be anything other than projectile motion through space, which of course would indeed require an enormous amount of energy.
Transporting matter at relativistic velocities requires energy. Transporting matter is the topic of the OP and the thread. If you want to consider some sort of non-material travel (astral projection or whatever), that's fine, but it is not the topic of the OP. If you want to imagine a universe where all of the laws of physics are completely different than ours, that's fine, too. But it is completely disconnected from reality. It is pure fantasy.

This message is a reply to:
 Message 11 by Taz, posted 10-30-2009 12:20 PM Taz has replied

Replies to this message:
 Message 15 by Perdition, posted 10-30-2009 2:09 PM kbertsche has replied
 Message 30 by Taz, posted 11-02-2009 12:51 AM kbertsche has replied

  
kbertsche
Member (Idle past 2122 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 16 of 81 (533452)
10-30-2009 7:45 PM
Reply to: Message 15 by Perdition
10-30-2009 2:09 PM


Re: fantasy
quote:
The science at one time said breaking the sound barrier was impossible,
This was no doubt a commonly-held conception, and it was certainly a technological challenge. But can you point to a reference where science said this was impossible?
quote:
As I said earlier in the thread, wormholes, space warping, etc may get us great distances in short times by altering the fabric of space itself to make the trip shorter. While this may seem "far-out" and "fantasy" there are physicists working on this sort of thing.
String theorists are certainly trying to understand these things in a fundamental, theoretical way. But can you point to any physicists who are actually "working on this sort of thing" with a goal "to make the trip shorter" for human transportation?

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 Message 15 by Perdition, posted 10-30-2009 2:09 PM Perdition has replied

Replies to this message:
 Message 34 by Perdition, posted 11-02-2009 1:29 PM kbertsche has replied

  
kbertsche
Member (Idle past 2122 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 22 of 81 (533510)
10-31-2009 12:49 PM
Reply to: Message 19 by Michamus
10-31-2009 8:01 AM


quote:
I understand what you are saying, and it makes sense. My question kind of assumes that we would be at a Stage of Technological Understanding to where manipulating the energy of stars is about as amazing as plugging in a toaster. (That's not a statement of possibility or probability, just a given necessary to discuss the point further)
Yes, if we were at such a point technologically, such travel would be simple.
quote:
I'm not too sure on the precision of your numbers, but I'll take them on good faith.
They are back-of-the-envelope calculations (literally), and should be accurate to 10% or so.
quote:
What exactly would be bad about traveling at 1G for 1 year? We experience 1G all the time for many years... In this scenario I would make the space-craft essentially accelerate floor side down, so you would have gravity in space.
There's nothing wrong with 1G at all for an entire lifetime, of course. But this only gets you to about 0.7 c after a year, where things are just starting to get relativistic. It would be preferable to accelerate at 2G or more to further reduce the time.
quote:
I'd imagine though that kind of acceleration would require quite a bit of energy to be sustained...
Exactly. This is the fundamental problem. It puts a very high cost on the process, and this would be true for any society where energy cost is at all significant.
These things are fun to speculate about, but they are not realistic in the foreseeable future. They certainly are not realistic until/unless we solve our energy problems. I am frankly surprised at the resistance that such comments meet in this thread. There seems to be a quasi-religious conviction here that mankind will be able to do such things one day. I consider these sci-fi speculations to be in the same vein as (but even less realistic than) global floods or vapor canopies.

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 Message 19 by Michamus, posted 10-31-2009 8:01 AM Michamus has not replied

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 Message 26 by Coyote, posted 10-31-2009 3:19 PM kbertsche has seen this message but not replied

  
kbertsche
Member (Idle past 2122 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 23 of 81 (533511)
10-31-2009 1:08 PM
Reply to: Message 20 by cavediver
10-31-2009 8:09 AM


quote:
Nothing - if you can accelerate hard enough and safely enough, you can reach Alpha C as fast as you like - couple of days maybe. Of course, your round trip as measured by someone on Earth will take 8.6 years, but you can do it so to age as little as you choose.
Yes, but it's not possible to accelerate hard enough and safely enough to reduce this to a few days. Jet pilots in pressurized suits can endure a few Gs (less than 10?) for very short periods. Even if you could somehow get to 12G's, it would still take a month to get to 0.7 c where things begin to get relativistic.
I invite you guys to check my back-of-the-envelope math. Here's a brief explanation of it:
1G acceleration is about 10 m/s^2. 1 year is about 3x10^7 seconds. So in a non-relativistic world, 1G for 1 year would take you to a velocity of 3x10^8 m/s. This just happens to be the speed of light, making things convenient. We haven't actually gotten to this velocity, of course, because of relativistic effects which we have ignored. But with a fixed force of acceleration for a year, we HAVE imparted the same momentum as in the non-relativistic case, a momentum equal to c times the rest mass (p = m0c). The total energy is then sqrt(2) times the rest energy, and the velocity is 0.7 c.
Edited by kbertsche, : clarified?

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Replies to this message:
 Message 24 by DevilsAdvocate, posted 10-31-2009 1:35 PM kbertsche has replied
 Message 31 by Taz, posted 11-02-2009 1:06 AM kbertsche has replied

  
kbertsche
Member (Idle past 2122 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 25 of 81 (533518)
10-31-2009 2:22 PM
Reply to: Message 24 by DevilsAdvocate
10-31-2009 1:35 PM


quote:
If we have enough energy to push a spacecraft to near c velocities I don't think using some of this energy to counteract g-forces would be much of an issue i.e. utilizing a rotating wheel like in 2001: A Space Odyssey, etc.
Correct me if I am wrong.
Centrifugal force from a rotating wheel can only add acceleration; it can't reduce it. This only makes things worse.

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 Message 24 by DevilsAdvocate, posted 10-31-2009 1:35 PM DevilsAdvocate has replied

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kbertsche
Member (Idle past 2122 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 38 of 81 (533739)
11-02-2009 4:00 PM
Reply to: Message 30 by Taz
11-02-2009 12:51 AM


Re: fantasy
I wrote:
Transporting matter at relativistic velocities requires energy.
quote:
There you go again, trapped in 16th century way of thinking. After all, people from the age of sail never thought using fossil fuel in a certain way in combination of aerodynamics would allow people to travel from Europe to America in a day.
Basically, instead of allowing room for new innovations and discoveries on space-time travel that doesn't require the energy of an entire star, you insist on a closed minded approach that everything other than the standard model of projectile motion through space the way we currently understand physics is a fantasy.
My approach is not closed minded; rather, it is grounded in reality. Einstein theorized an equivalence between matter and energy and this has been experimentally verified. Hence my original comment. If you wish to transport matter at relativistic velocities without using a tremendous amount of energy, you would have to disprove Einstein's E=mc^2 relation and to explain why all of the experimental evidence of it is wrong. You are free to theorize about such fantasies as much as you wish.

This message is a reply to:
 Message 30 by Taz, posted 11-02-2009 12:51 AM Taz has not replied

  
kbertsche
Member (Idle past 2122 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 51 of 81 (533777)
11-02-2009 7:13 PM
Reply to: Message 31 by Taz
11-02-2009 1:06 AM


quote:
Imagine yourself and an object with a gravitational pull of 5 G pulling you toward it. Now, we accelerate you and the object at 6 G. You will only feel 1 G. Suppose the object is pulling you at 7 G and you both are accelerated at 8 G. You will still only feel 1 G.
Dwelling on this thought, suppose we possess neutron matter. The neutron matter is put in front of the ship. The more the ship accelerates, the closer you are automatically put toward the neutron mass. When you decelerate, the ship automatically pulls you away from the neutron matter.
In which case you are not only accelerating the spaceship, but also the mini-neutron star. This takes immensely more energy than just accelerating the spaceship, only reinforcing the point that you would need a new, inexpensive energy source first. Also, the "neutron matter" needs to be far enough in front of the spaceship that its gravity gradient won't rip the ship and people apart.

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 Message 52 by Coyote, posted 11-02-2009 7:18 PM kbertsche has seen this message but not replied

  
kbertsche
Member (Idle past 2122 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 53 of 81 (533789)
11-02-2009 8:24 PM
Reply to: Message 34 by Perdition
11-02-2009 1:29 PM


Re: fantasy
quote:
But by claiming that we must travel through space the same way we do now is short-sighted and mired in the thinking of the past/present without considering new advances and discoveries that may be just over the horizon.
It would be foolish to lock one's predictions to present-day technology. But it is equally foolish to think that our experimentally-verified understanding of relativity is completely wrong. And if our understanding of relativity is basically correct, physical travel (i.e. transportation of matter) with large accelerations requires a large amounts of energy. Like it or not, new technologies, new energy sources, or new physics cannot change this. The only way to change this is to disprove our experimentally-verified theories of relativistic dynamics.

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 Message 34 by Perdition, posted 11-02-2009 1:29 PM Perdition has not replied

Replies to this message:
 Message 59 by RickJB, posted 11-03-2009 5:24 PM kbertsche has replied

  
kbertsche
Member (Idle past 2122 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 63 of 81 (533952)
11-03-2009 8:29 PM
Reply to: Message 59 by RickJB
11-03-2009 5:24 PM


Re: fantasy
quote:
Furthermore, the current theories we have need not be proven completely incorrect to accommodate new possibilities. For example, just as Einstein modified Newtonian mechanics, so shall someone in the future modify Relativity.
Yes, Newtonian mechanics is still an excellent approximation over the parameter space where it was experimentally verified. And I expect Einsteinian relativity will likewise remain an excellent approximation over the parameter space where it has been experimentally verified. Thus there is no realistic hope of physical travel to distant planets without a tremendous expenditure of energy.

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 Message 59 by RickJB, posted 11-03-2009 5:24 PM RickJB has replied

Replies to this message:
 Message 66 by RickJB, posted 11-04-2009 7:45 AM kbertsche has seen this message but not replied

  
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